Interactions for exposure to fine particulate matter and multiple time-period cold spells on influenza: A...

With the increasing twin threats of climate change and air pollution, cumulating evidence has revealed that environmental exposure might promote influenza epidemic. However, it remains unclear whether the combination of air pollution and cold spells (CS) synergistically trigger influenza. Through a case-crossover study, we included 13,972 laboratory-diagnosed influenza patients in Hubei province, China, during 2011-2018. We then constructed the conditional logistic regression model to assess the adverse impact of overall-, daytime-, and nighttime-CS exposure, as well as PM_2.5 pollution, on influenza, and further calculated their additive-scale interactions. Our results indicated that both PM_2.5 and CS were associated with influenza. For an interquartile range increment of PM_2.5 was associated with 8 % [odds ratio = 1.08, 95 % confidence interval (CI): 1.04-1.12] increased risk of influenza. The estimated risks of overall-, daytime-, and nighttime-CS exposure on influenza were 1.18 (95 %CI: 1.12-1.23), 1.16 (95 %CI: 1.08-1.25), and 1.28 (95 %CI: 1.19-1.38), respectively. Calculated population attributable fractions were ranged from 1.13 % to 4.42 %. Significant synergetic effects on influenza were observed for co-exposure to PM_2.5, CS, indicated by relative excess risk due to interaction of 0.23 (overall-CS) and 0.26 (nighttime-CS). Exposure to both PM_2.5 and CS, especially nighttime-CS, were associated with influenza, and PM_2.5 and CS could interact synergistically trigger influenza epidemic.